A garden is nothing without a good foundation, and that foundation is the soil. Soil has its own complicated ecosystem from worms and beetles on down to tiny, nearly-microscopic filaments of fungi and bacteria. As with anywhere on earth, a healthy ecosystem is essential for optimal growth and health.
In my backyard the soil is a heavy clay over a base of sand. It barely grows grass in some places. But, if you build it they will come... The raised bed that I put in last summer is nearly overflowing with worms, and centipedes are fairly common, too, much to my husband's chagrin. It started off life as a lasagna garden, with a base layer of cardboard boxes recycled after the move, a couple bags of dirt from the grocery store garden center, and some trench-compost piles. Now there's enough good dirt to grow short-ish carrots, and my herbs are taking off. The bed isn't very large because it takes a fair input of cash to start that way, with the boards and hardware to attach the corners. I used two un-treated cedar deck planks and cut them down to a rectangle.